Food technologists have over the years strived to develop synthetic or natural flavors which would either impart a coffee-like flavor to an imitation beverage or a flavor which would augment a particular flavor note in a natural coffee product in which the flavor note was deficient. A compound in coffee which imparts a butter flavor and aroma is the compound diacetyl (2, 3-butanedione). This compound is a yellow liquid having an extremely potent butter aroma. Diacetyl can be formed either by chemical synthesis or by bacterial fermentation. Diacetyl as a flavorant is particularly important in dairy products such as sour cream, and cultured butter and butter milk. Also it is important in such non-dairy products as butterscotch, honey, coffee, maple syrup, white bread, summer sausage, and margarine.
U.S. Pat. No. 4,304,862, issued to Troller entitled "Method for Increasing the Diacetyl Production of a Diacetyl-Producing Bacteria" teaches a method wherein the increased diacetyl production is attributable to a set of specific conditions including a nutrient medium having a pH of from about 4.5 to 7, incorporation of a humectant to lower the a.sub.w value of the nutrient medium to about 0.95 to 0.99 and a temperature for incubation of from about 28.degree. to 37.degree. C. The patent also teaches incorporating a metabolizable amount of a diacetyl precursor which is citric acid or an acceptable salt thereof. An article written by Collins in The Journal of Dairy Science entitled "Biosynthesis of Flavor Compounds by Microorganisms" teaches that the enhancement of diacetyl production requires a strain of bacteria or yeast able to produce diacetyl, and the control of the environment such as to achieve good growth of the selected organism. Specifically the environment includes a pH below about 5.5 and an oxygen containing environment.
While diacetyl has been known as an important flavor ingredient of dairy and coffee products, fermentation produced by bacteria or yeast on a coffee substrate to produce a natural diacetyl has not heretofore been demonstrated. It is an object of the present invention to produce diacetyl by microbial fermentation of pure coffee materials to produce a buttery flavor directly from a coffee substrate.